ABSTRACT
Background/Aims@#The abscopal effect, a rare phenomenon induced by radiation, can be reinforced by immunotherapy. Although radiation therapy and immunotherapy are increasingly being utilized for the treatment of hepatocellular carcinoma (HCC), whether immunotherapy could boost the abscopal effect remains unclear. In this study, we aimed to elucidate the immunological mechanisms underlying the abscopal effect induced by the combination of irradiation and immunotherapy in a murine HCC model. @*Methods@#A syngeneic HCC mouse model was established by transplanting murine Hepa 1–6 HCC cells into both hind legs of immunocompetent C57BL/6 mice. The tumors on the right hind legs were irradiated, and abscopal effects were observed in the non-irradiated tumors on the left hind leg with or without the coadministration of anti-programmed cell death 1 (PD-1) antibodies. Flow cytometric analyses were performed to analyze the distributions of immune cells infiltrating both irradiated and non-irradiated tumors and the tumor-draining lymph nodes (TDLNs). @*Results@#Administration of 16 Gy in two fractions more effectively inhibited the growth of both irradiated and nonirradiated tumors with higher tumor infiltration of cytotoxic T cells than 8 Gy did in a single fraction. The higher dose also increased activated dendritic cells in TDLNs, which had higher expression of the programmed cell death ligand 1. Coadministration of anti-PD-1 antibodies significantly enhanced the abscopal effect and increased infiltration of activated cytotoxic T cells in both irradiated and non-irradiated tumors. @*Conclusions@#Our findings show that adding anti-PD-1 therapy to radiation enhanced the abscopal effect in a syngeneic murine model of HCC.
ABSTRACT
PURPOSE: This study is to investigate the effect of captopril when combined with irradiation. MATERIALS AND METHODS: 4T1 (mouse mammary carcinoma) cells were injected in the right hind leg of Balb/c mice. Mice were randomized to four groups; control (group 1), captopril-treated (group 2), irradiated (group 3), irradiated and captopril-treated concurrently (group 4). Captopril was administered by intraperitoneal injection (10 mg/kg) daily and irradiation was delivered on the tumor-bearing leg for 15 Gy in 3 fractions. Surface markers of splenic neutrophils (G-MDSCs) and intratumoral neutrophils (tumor-associated neutrophils [TANs]) were assessed using flow cytometry and expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1 alpha (HIF-1α) of tumor was evaluated by immunohistochemical (IHC) staining. RESULTS: The mean tumor volumes (±standard error) at the 15th day after randomization were 1,382.0 (±201.2) mm³ (group 1), 559.9 (±67.8) mm³ (group 3), and 370.5 (± 48.1) mm³ (group 4), respectively. For G-MDSCs, irradiation reversed decreased expression of CD101 from tumor-bearing mice, and additional increase of CD101 expression was induced by captopril administration. Similar tendency was observed in TANs. The expression of tumor-necrosis factor-associated molecules, CD120 and CD137, are increased by irradiation in both G-MDSCs and TANs. Further increment was observed by captopril except CD120 in TANs. For IHC staining, VEGF and HIF-1α positivity in tumor cells were decreased when treated with captopril. CONCLUSION: Captopril is suggested to have additional effect when combined to irradiation in a murine tumor model by modulation of MDSCs and angiogenesis.